Realistic MG-1 dead keys

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stellarsoundlabs
Posts: 1
Joined: Mon Sep 13, 2021 6:03 pm

Realistic MG-1 dead keys

Post by stellarsoundlabs » Wed Oct 20, 2021 10:29 am

Following the excellent service manual, I'm finishing up the repairs & mods of a Realistic MG-1. I've got many hours into this, and it's almost 100%.

I've replaced the 3 MM5823's with the daughterboards from tauntek.com and the TO83 with the daughterboard from Flatkeys UK. This cleared up several 'dead' keys but 4 still remain. (Key contacts are ok.)

These 4 keys seem to create triggers but produce no sound:

E3 - scoping U2003 pin 11 looks ok (proper square wave)
F#2 - U2005-10 ok
F#3 - U2005-9 latched at +12VDC (possible short from soldering the 5823 daughterboard?)
A#3 - U2003-9 ok

I notice that within U1009 some voltages are off +/-10%. I'm not sure if that's an issue. The "dead" keys are ok at Tone Src outs/VCO faders but are not making it into U10 (or U13).

Please note that U1001-2 & U1004-2 look ok (scope shows proper voltages). U1002-5 ok. U1005-3 ok. U1006 TS ok. U1007A T&H ok.

I've been over and over the schematic checking every test point. I would love any advice on what to check next. Thank you.

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